JP3176582B2 - Recording and erasing information - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording and erasing information, and more particularly to a method using a phase-change type information recording medium. The present invention relates to a method of using a rewritable information recording medium for performing recording and reproduction, and is applied to an optical memory related device.

[0002]

2. Description of the Related Art As one of optical memory media capable of recording / reproducing and erasing information by irradiating an electromagnetic wave, particularly a laser beam, a so-called phase change type utilizing a transition between a crystal and an amorphous phase or between a crystal and a crystal phase. Recording media are well known. In particular, overwriting with a single beam, which is difficult with a magneto-optical memory, is possible, and the drive-side optical system is simpler. USP3, 53
0,441, Ge-Te, Ge-
Te-Sb-S, Ge-Te-S, Ge-Se-S, G
e-Se-Sb, Ge-As-Se, In-Te, Se
And so-called chalcogen-based alloy materials such as -Te and Se-As. In addition, for the purpose of improving stability, high-speed crystallization, etc.
Au (Japanese Patent Application Laid-Open No. 61-21992), Sn and Au (Japanese Patent Application Laid-Open No. 61-270190), Pd (Japanese Patent Application Laid-open No.
2--19490) and the like, and for the purpose of improving the repetition performance of recording / erasing, Ge-Te-Se-Sb
There has been proposed a material (JP-A-62-73438) in which the composition ratio is specified. However, none of them can satisfy all of the characteristics required for a phase-change rewritable optical memory medium.

Further, Japanese Patent Application Laid-Open No. 63-251290 proposes an optical recording medium having a recording layer composed of a single phase of a multi-component compound having a ternary or higher crystalline state. Here, a ternary or higher ternary compound single phase is defined as a compound having a ternary or higher stoichiometric composition (for example, In ₃ SbTe ₂ ) in a recording layer of 90 atomic% or more.

By using such a recording layer, high-speed recording and high-speed erasing can be performed.

However, the laser power required for recording and erasing is not yet sufficient. It has disadvantages such as a low erasure ratio (large erasure remaining).

Further, in Japanese Patent Application Laid-Open No. 1-277338, (Sb _X Te _{1 -X} ) _{1 -Y} M _Y (where 0.4 ≦ X <0.7,
Y ≦ 0.2, M is Ag, Al, As, Au, Bi, C
u, Ga, Ge, In, Pb, Pt, Se, Si, Sn
And at least one selected from the group consisting of Zn and Zn)
An optical recording medium having a recording layer made of an alloy having a composition represented by the following formula has been proposed.

The basis of this system is Sb ₂ Te _3. Excessive Sb improves high-speed erasure and repetition characteristics, and addition of M promotes high-speed erasure. D
The erasure rate by C light is also large.

However, the erasure rate at the time of overwriting is not shown (the result of the study by the present inventor has left unerased data), and the recording sensitivity is insufficient.

Similarly, Japanese Patent Application Laid-Open No. Sho 60-177446 discloses that (In _{1 -X} Sb _x ) _{1 -Y} M _Y (0.55 ≦ X ≦ 0.8
0, 0 ≦ Y ≦ 0.20).
The recording layer in 228433 GeTe-Sb ₂ Te ₃ -Sb
Although (excess) alloys are used, they do not satisfy characteristics such as sensitivity and erasing ratio.

Japanese Patent Application Laid-Open No. 63-173241 proposes a recording layer in which a recording material is dispersed in a thermally stable matrix.

However, the matrix materials are all high melting point materials having high translucency, and the recording layer as a whole cannot obtain sufficient light absorption and reflectance, resulting in a decrease in sensitivity, contrast and the like. Also, the one-beam overwrite performance is not sufficient.

In particular, improvement of recording sensitivity and erasing sensitivity, prevention of a decrease in erasing ratio due to unerased data during overwriting, and prolongation of life of a recorded portion and an unrecorded portion are the most important issues to be solved.

Among them, the laser irradiation time is 100 nsen
Regarding the laser writing power on the medium surface under the following conditions, all of the reported examples up to now require a power of about 15 mW or more, which is a major barrier for improving the transfer speed. In addition, the heat generated at the time of repeated recording / erasing damages the recording layer, the heat-resistant protective layer, and the like, and causes deterioration of the characteristics.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for recording and erasing information using an information recording medium in which the following points are improved as compared with the above prior art.

(1) Improvement of laser writing (recording) sensitivity, (2) improvement of erasure sensitivity, (3) improvement of repetition performance of recording and erasure, and (4) improvement of erasure ratio.

[0016]

In order to solve the above-mentioned problems, it has been found that it is extremely effective to use the following substances as a recording layer material of a phase change type information recording medium.

The main component of the recording layer provided on the substrate has a phase (M phase) in which a phase transition between crystal and amorphous or between crystal and crystal occurs during recording / erasing, and no phase transition occurs during recording / erasing. An information recording medium that exists in a mixed state with a phase (L phase), and the M phase and the L phase satisfy the following conditions.

L _1−a + M _a (0.30 ≦ a ≦ 0.92) Melting point of M ≦ 700 ° C. Melting point of L> Melting point of M Each of the M phase and the L phase for an electromagnetic wave having a wavelength used for recording / erasing. The light absorption coefficients α _M and α _L are α _M ≧ 10 ³ cm- ¹ and α _L ≧ 10 ² cm- ¹ where α is I = I _O (1-R) ² exp ~ ^α1 I _O : incident light intensity I : Transmitted light intensity l: Film thickness R: Reflectance α _M is preferably 5 × 10 ³ cm to ¹ or more, most preferably 1 × 10 3
⁴ cm to ¹ or more, α _L is preferably 1 × 10 ³ cm to ¹ or more, and most preferably 5 × 10 ³ cm to ¹ or more.

Further, L is desirably a compound composition of two or more components or a composition in the vicinity thereof in order to improve the repetition performance. The M phase and the L phase need to be in a mixed phase, but it is desirable that the M phases, which are phase transition phases, are completely separated by the L phase. In that case, the average size of the exfoliated M phase (hereinafter, referred to as fine particle diameter) is 30 to 500 °,
Preferably it is between 50 and 300 °, optimally between 80 and 200 °. The content a of M is 0.30 ≦ a ≦ 0.92, preferably 0.50 ≦ a ≦ 0.90, and most preferably 0.60 ≦ a ≦
0.90.

Further, the melting point of M is 700 ° C. or less, preferably 6 ° C.
The temperature is preferably 50 ° C. or less, most preferably 600 ° C. or less.

The accompanying drawings show the present recording layer in a simplified and schematic manner.

The phase change phase (M phase) 1 forms a mixed phase in a state of being dispersed in the non-phase change phase (L phase) 2 forming a matrix. As the M phase, for example, Sb (m.
p. 630 ° C.), and AgInTe ₂ (m.
p. 680 ° C).

With such a configuration, the recording layer has the following characteristics.

(1) Phase transition phase (M phase), non-phase transition phase (L
Both phases have light absorbing ability, so that the use efficiency of electromagnetic waves (for example, LD light) at the time of recording / erasing increases. as a result,
The sensitivity is improved.

(2) Since the M phase exists in a fine particle state,
The melting point is lower than the value in the bulk state. Therefore, it is possible to reduce the energy required at the time of amorphous recording (usually melting / quenching). That is, recording sensitivity and response speed are improved.

In addition, sensitivity and response speed are improved during recrystallization (erasing).

Among them, it has been found that an extremely large improvement can be achieved particularly by using an information recording medium containing a substance represented by the following general formula as a main component as a recording layer material.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the information recording medium is as follows: (1) The main component of a recording layer provided on a substrate is represented by the following general formula, and the presence state in the recording layer is XYZ ₂ phase and M An information recording medium characterized by being a mixed phase with a phase.

The general formula (XYZ ₂ ) _{1- a} Ma XYZ ₂ is represented by Ib-IIIb-VIb ₂ or IIb-I in the periodic table.
Chalcopyrite-type compound represented by the Vb-Vb _2, M
Is one or more elements selected from Sb, Bi, S, Se, and Te, or AgSbTe ₂ , where 0.30 ≦ a ≦ 0.92.

(2) XYZ ₂ is AgInTe ₂ and M
Is Sb or Bi, the information recording medium according to the above (1).

If a is less than 0.3 or more than 0.92, there is no effect on improving sensitivity, erasing ratio and contrast.

In the recording layer, a trace amount of other impurities (1
% Or less).

Further, the present invention includes the following items as its embodiments.

A) An information recording medium in which the L phase is a binary compound or more.

B) The main component of the recording layer provided on the substrate is represented by the following general formula, and the presence state in the recording layer is XY
An information recording medium which is a mixed phase of Z ₂ phase and M phase. The general formula (XYZ ₂ ) _{1- a} Ma XYZ ₂ is represented by Ib-IIIb-VIb ₂ or IIb-I in the periodic table.
Arco pyrite type compound represented by the Vb-Vb _2, M
Is at least one element selected from Sb, Bi, S, Se and Te or AgSbTe ₂ , 0.30 ≦ a ≦ 0.92 c) XYZ ₂ is AgInTe ₂ and M is Sb or Bi
The information recording medium according to the above item b), wherein

[0036] d) above b) or c) the general formula in claim (XYZ ₂₎ results material represented by _1-a M a is contained traces of oxygen, the general formula (XYZ ₂₎ in _1-a M a instead _{{(XYZ 2) 1-a} M a} 1-b O b ( however, 0.01 ≦ b ≦ 0.30, and other symbols are b) above b) the term or c represented by the same) and section) It is an information recording medium described in the section.

Specific examples of XYZ ₂ include: Ib-IIIb-VIb ₂ ; AgInTe ₂ , AgInSe ₂ ,
AgGaSe ₂ , AgInS ₂ , CuInTe ₂ , CuI
nSe ₂ IIb-IVb-Vb ₂ ; ZnSnSb ₂ , ZnSnAs ₂ ,
ZnSnP ₂ , ZnGeAs ₂ , CdSnP ₂ , CdSn
As _{2 and the} like.

XYZ ₂ preferably has a stoichiometric composition, but each may have a slight composition deviation.

[0039] Specifically, X _o Y _p Z when the _{q 0.2 ≦ o ≦ 0.3 0.2 ≦} p ≦ 0.3 0.4 ≦ q ≦ 0.6 o + p + q = 1.0

[0040]

When the recording layer of the present invention is irradiated with a laser beam, it is considered that the following phase transition occurs depending on the irradiation conditions.

For simplicity, Ag is used as XYZ ₂
A description will be given taking InTe ₂ as an example and S as S as an example.

Amorphous and / or Chalcop of AgInTe ₂
The crystal-to-crystal and / or crystal-to-amorphous and / or microcrystalline-coarse crystal transition (MgInTe in this case) of M (Sb in this case) in the yrite type structure and / or the Zincblende type structure.
₂ makes the transition easy and stable).

Although the mechanism of the phase transition cannot be clearly specified by only the information obtained at present, in any case, A
The following points were found to be particularly excellent as compared with the case where gInTe ₂ and Sb exist alone.

(1) The light absorptivity is increased, and the recording / erasing sensitivity is improved.

(2) The optical contrast before and after the transition is increased, and the C / N is improved.

(3) The erasing ratio during overwriting is dramatically improved.

With regard to the erasing characteristics in particular, surprisingly, almost complete erasing was possible not only in simple erasing with DC light but also in one-beam overwrite mode.

This is a performance not found at all in any of the materials known to date.

Next, the case where the AgSbTe ₂ -based phase is the M phase will be described as an example.
The SbTe ₂ -based phase (M phase) and the L-based phase exist in a mixed phase. There are several methods for obtaining such a mixed phase. For example, Ag, S by a film forming method such as sputtering.
It is obtained by forming a thin film containing b and Te on a substrate and subjecting it to a heat treatment to phase-separate AgSbTe ₂ and the L phase. Examples of the heat treatment method include a method using a laser beam and a method using a heater. The use of a laser beam is preferable because the heat treatment conditions can be arbitrarily selected by controlling the laser beam intensity and the number of rotations by rotating the disk.

When a laser beam having a recording power (Pw) is irradiated, the AgSbTe ₂ phase undergoes a phase transition from a crystal to an amorphous phase, and the other L phase of the mixed phase (the crystal phase at the time of recording and erasing). The phase that is made of a material that does not cause a phase transition between amorphous states always maintains the amorphous state.

When a laser beam having an erasing power (P _E ) is irradiated, the AgSbTe-based phase undergoes a phase transition from amorphous to crystalline, and the L phase enters the amorphous state without causing a phase transition. maintain.

Although the L phase is amorphous in this example, the L phase may be crystalline. In this example, AgSbTe ₂
The phase may be in an amorphous state as a recording state, and conversely, a crystalline state may be in a recording state.

In any case, the AgSbTe ₂ phase and the L phase are in a so-called mixed phase.

As the L phase, those having a light absorption coefficient of 10 ² cm to ² or more are desirable, and specific examples thereof include In-Sb
System, In-Sb-Te system, Sb-Te system, In-Te
System, Ge-Sb system, Ge-Te system, Ge-Sb-Te system and the like.

In the present invention, no phase change occurs in any case of the L phase as described above, and the AgSbTe ₂ phase
Due to the phase transition of the amorphous phase, the reflectivity of the disk changes, and recording / erasing is performed here, and an extremely high erasing ratio can be obtained.

Although the mechanism for obtaining a high erase ratio is not always clear, it can be considered as follows. Since AgSbTe ₂ is originally a substance that is easily crystallized, covering it with the non-phase transition phase L is expected to have an effect of facilitating recording (amorphization). The mechanism is considered as follows.

A for the L phase over AgSbTe ₂
Ordering of gSbTe ₂ is less likely to occur.

By controlling the thermal conductivity of the recording layer in the L phase while maintaining the characteristics of AgSbTe ₂ to some extent, the rapid cooling condition is satisfied during recording. In this case, it is desirable that the L phase has a higher thermal conductivity than AgSbTe ₂ .

Further, by covering the AgSbTe ₂ phase with the L phase, the particle size of AgSbTe ₂ can be kept constant, and the repetition reliability can be improved.

As can be seen from the general formula, in the recording layer of the present invention, the amount of the AgSbTe ₂ phase is considerably larger than the amount of the L phase. That is, the former AgS
The amount of BTE ₂ phase accounts for 30-92% of the total multiphase. In the above general formula, if the value of a is less than 30% or exceeds 92%, the effect of improving the erase ratio cannot be recognized. Further, the recording layer may contain a small amount (1% by weight or less) of another impurity (for example, oxygen or the like).

That is, the fact that a high erasing ratio can be obtained means that, when an erasing operation is performed on the recording portion, crystallization or amorphization proceeds in a form completely covering the recording portion. ing. Therefore, a large amount of uniform nucleation and growth of AgSbTe ₂ first proceed in the amorphous or crystalline recording portion, and in parallel with this, heterogeneous nucleation and growth of AgSbTe ₂ proceed from the surface of the amorphous L phase. It is thought that the process of doing this has occurred.

According to the recording layer of the present invention,
(1) The light absorptance is increased, and the recording / erasing sensitivity is improved. (2) The optical contrast before and after the transition is increased to improve the C / N. (3) The erasing ratio during overwriting is dramatically increased. It was also recognized that it improved.

The optical information recording medium of the present invention basically comprises
Such a recording layer has a thickness of 200 to 10000Å, preferably 5
00-3000Å, more preferably 700-2000Å
It is made of a thick material formed on a substrate.

The information recording medium of the present invention may be provided with auxiliary layers such as a heat-resistant protective layer, a surface protective layer, a reflective layer, a heat dissipation layer, and an adhesive layer, if necessary.

The substrate used in the present invention is usually glass,
Ceramic or resin, the resin substrate is moldable,
It is suitable in terms of cost and the like. Representative examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin and the like. Polycarbonate resins and acrylic resins are preferred in view of workability, optical properties and the like. The shape of the substrate may be a disk shape, a card shape or a sheet shape.

As the material of the heat-resistant protective layer, SiO, S
iO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O
₃ , metal oxides such as MgO, ZrO ₂ , Si ₃ N ₄ , Al
Nitride such as N, TiN, BN, ZrN, ZnS, In ₂
S _3, TaS sulfides such as _{4, SiC, TaC, B 4} C, W
Examples thereof include carbides such as C, TiC, and ZrC, diamond-like carbon, and mixtures thereof. Further, it may contain impurities as needed. Such a heat-resistant protective layer can be formed by various vapor deposition methods, for example, a vacuum deposition method, a sputtering method,
It can be formed by a plasma CVD method, a photo CVD method, an ion plating method, an electron beam evaporation method, or the like.

The thickness of the heat-resistant protective layer is 200 to 50.
00 °, preferably 500-3000 °.
When the thickness is less than 200 °, the function as a heat-resistant protective layer is not fulfilled. On the other hand, when the thickness is more than 5000 °, the sensitivity is lowered and the interface is liable to peel off. Further, if necessary, the protective layer can be multi-layered.

A that serves as both the reflection layer and the heat radiation layer is A
l, Au and other thin films (thickness of about 200-2000mm)
Is used.

The phase change material is not limited to a single layer, but may be a multilayer film or an ultrafine particle in which the phase change material according to claim 1 is dispersed in a heat resistant matrix.

As a method for producing the recording film as the latter, a wet process such as a sol-gel method can be applied in addition to the vapor phase film formation.

Among the vapor deposition methods, a high frequency (rf) sputtering method is a preferable method in terms of film characteristics, ease of film formation, and the like.

Typical conditions for forming the recording layer in the rf sputtering method are as follows: target: XYZ ₂ + M (for example, AgInTe ₂ + S
b) ・ Sputtering (reaction) pressure: 0.5 to 20 Pa ・ rf power: 20 W to 1 kW ・ Sputtering gas: Ar + (O ₂ : when controlling the amount of oxygen in the film) ・ Sputtering time: 10 seconds to 20 minutes However, the production method and conditions are not limited at all.

The thickness of the recording layer is 200 to 10,000.
0 °, preferably 500-3000 °, optimally 700-
2000 $.

Various electromagnetic waves such as laser light, electron beam, X-ray, ultraviolet ray, visible light, infrared ray, and microwave can be used for recording, reproducing and erasing. A compact semiconductor laser beam is optimal.

[0075]

The present invention will be specifically described below with reference to examples. However, these examples do not limit the present invention at all.

Example I-1 A groove having a pitch of 1.6 μm and a depth of 700 °, a thickness of 1.2 m
A heat-resistant protective layer, a recording layer, a heat-resistant protective layer, and a reflective layer were sequentially laminated on an m, 86 mmφ polycarbonate substrate by rf sputtering to produce an optical disc for evaluation. The materials and film thicknesses used for each layer are shown in Table I-1 below.

The optical disk was evaluated by passing a 830 nm semiconductor laser beam through the lens of NA 0.5 at 1 μm on the medium surface.
This was performed by narrowing down to a spot diameter of φ and irradiating from the substrate side.

Although the recording film after film formation was amorphous, at the time of measurement, the entire surface of the disk was first sufficiently crystallized with 4 to 10 mW of DC light on the medium surface, and the medium was initialized (unrecorded). And The linear velocity of the disk was 7 m / s.

The recording conditions were such that the linear velocity was 7 m / s, the frequency was constant at 3.7 MHz, and the laser power (P _W ) was varied from 7 to 14 mW.

The reading power (P _R ) was set to 1.0 mW. Table I shows the laser power (P _W ) and the optimum erase power (P _E ) when the C / N (carrier-to-noise ratio) value is saturated or maximum, and the obtained C / N value and erase ratio.
-1.

Further, for a disk having a C / N value of 45 dB or more and an erasing ratio of 35 dB or more, two writing frequencies (f ₁ = 3.7 MHz and f ₂ = 4.5 MHz) are used.
An overwrite test was performed alternately.

Write power during overwrite (P _W )
The optimum value of the erasing power (P _E ) was selected depending on the disc.

[0083] line speed, P _R, etc., other conditions were the same as those of the time of writing test.

The results of overwrite performance are shown in Table I-2 below.
Shown in

From Tables I-1 and I-2, it is confirmed that the phase change type optical recording medium according to the present invention has excellent performance, and particularly, high sensitivity is achieved in terms of recording sensitivity.

[0086]

[Table 1]

[0087]

[Table 2]

Example I-2 The write performance was tested under the same conditions as in Example I-1, except that the layer configuration was changed. The results are shown in Table I-3 below.

The overwrite performance was tested under the same conditions as in Example I-1. The results are shown in Table I-4 below.

[0090]

[Table 3]

[0091]

[Table 4]

Example I-3 As in Example I-2, the write performance was tested under the same conditions as in Example I-1, except that the layer configuration of Example I-1 was changed. The results are shown in Table I-5 below.

The overwrite performance was tested under the same conditions as in Example I-1. The results are shown in Table I-6 below.

[0094]

[Table 5]

[0095]

[Table 6]

Example II-1 A groove having a pitch of 1.6 μm and a depth of 700 °, a thickness of 1.2 m
A heat-resistant protective layer, a recording layer, a heat-resistant protective layer, and a reflective layer were sequentially laminated on an m, 86 mmφ polycarbonate substrate by rf sputtering to produce an optical disc for evaluation. Example
At the time of preparing the recording layer of II- (1, 2, 3), the oxygen concentration in the sputtering gas was adjusted to the flow ratio of O ₂ gas to Ar gas (O ₂ / Ar).
Was changed to obtain recording layers having different oxygen concentrations. The materials and film thicknesses used for each layer are shown in Table II-1 below.

The evaluation of the optical disk was conducted by passing a 830 nm semiconductor laser beam through a lens of NA 0.5 at 1 μm on the medium surface.
This was performed by narrowing down to a spot diameter of φ and irradiating from the substrate side.

Although the recording film after film formation was amorphous, at the time of measurement, the entire surface of the disk was first sufficiently crystallized with 4 to 10 mW of DC light on the medium surface, and the medium was initialized (unrecorded). And The linear velocity of the disk was 7 m / s.

The recording conditions were such that the linear velocity was 7 m / s, the frequency was constant at 3.7 MHz, and the laser power (P _W ) was varied from 7 to 14 mW.

The reading power (P _R ) was 1.0 mW. Table II shows the laser power (P _W ) and the optimum erase power (P _E ) when the C / N (carrier-to-noise ratio) value is saturated or maximum, and the obtained C / N value and erase ratio.
-1.

Further, for a disk having a C / N value of 45 dB or more and an erasing ratio of 35 dB or more, two writing frequencies (f ₁ = 3.7 MHz and f ₂ = 4.5 MHz) are used.
An overwrite test was performed alternately.

Write power at overwrite (P _W )
The optimum value of the erasing power (P _E ) was selected depending on the disc.

[0103] line speed, P _R, etc., other conditions were the same as those of the time of writing test.

The results of overwrite performance are shown in Table II-2 below.
Shown in

From Tables II-1 and II, it is confirmed that the phase change type optical recording medium according to the present invention has excellent performance, and particularly, high sensitivity is achieved in terms of recording sensitivity.

[0106]

[Table 7]

[0107]

[Table 8]

Example II-2 The write performance was tested under the same conditions as in Example II-1, except that the layer structure was changed. The results are shown in Table II-3 below.

The overwrite performance was tested under the same conditions as in Example II-1. The results are shown in Table II-4 below.

[0110]

[Table 9]

[0111]

[Table 10]

Example II-3 As in Example II-2, the write performance was tested under the same conditions as in Example II-1, except that the layer configuration of Example II-1 was changed. The results are shown in Table II-5 below.

The overwrite performance was tested under the same conditions as in Example II-1. The results are shown in Table II-6 below.

[0114]

[Table 11]

[0115]

[Table 12]

Example III-1, Comparative Examples III-1 and III-
2. A groove with a pitch of about 1.6 μm and a depth of about 700 ° has a thickness of 1.
A lower (substrate-side) heat-resistant protective layer, a recording layer, an upper heat-resistant protective layer, and a reflective layer were sequentially laminated on a 2 mm and 86 mm φ polycarbonate substrate by rf sputtering to produce three types of optical disks for evaluation.

The materials and film thicknesses used for each layer are shown in Table III-
1 is shown. In common, the lower heat-resistant protective layer is S
i ₃ N ₄ (about 2000 mm thick), S
i ₃ N ₄ (about 1000 mm thick) and Al (about 5
00Å).

The evaluation of the optical disc was performed by passing a semiconductor laser beam of 830 nm through a lens having an NA of about 0.5 on the recording layer surface.
This was performed by narrowing down the spot system of μmφ and irradiating it from the substrate side.

Although the recording layer after film formation was amorphous, at the time of measurement, the entire surface of the disk was first sufficiently crystallized with 4 to 10 mW of DC light at the time of measurement, and the recording layer was initialized (unrecorded). And The linear velocity of the disk was 7 m / s.

The recording conditions were such that the linear velocity was 7 m / s, the frequency was constant at 3.7 MHz, and the laser power (P _W ) was varied from 7 to 14 mW.

The reading power (P _R ) was set to 1.0 mW. The table also shows the laser power (P _W ) and the optimum erase power (P _E ) when the C / N (carrier-to-noise ratio) value is saturated or maximum, and the obtained C / N value and erase ratio. It is shown in III-1.

[0122]

[Table 13]

Subsequently, the overwrite characteristics were evaluated. The method consists of two writing frequencies f ₁ = 3.7 MHz,
Overwriting was performed alternately at f ₂ = 4.5 MHz. The optimum values of the write power (P _W ) and the erase power (P _E ) at the time of overwriting were selected depending on the disk. Other conditions were the same as in the writing test. Table III-2 shows the results.

[0124]

[Table 14]

Also, the recording portion of the overwritten recording layer,
When electron beam diffraction was performed on each of the erased portions, a broad ring pattern unique to amorphous was observed in the recorded portion. On the other hand, in the erased portion, in addition to the same ring pattern as that of the recording portion, a clear Bragg reflection point was observed, and it was confirmed from the plane interval that the crystal was AgSbTe ₂ .

[0126]

As described above, the effects of the present invention are summarized as follows.

(1) The heating temperature required for recording / erasing is low. Further, since the material of the present invention has a high light absorptivity, the recording layer heating efficiency during laser beam absorption is also high. For the above reasons, the required laser power can be reduced.
That is, the recording / erasing sensitivity is greatly improved.

(2) Since the required laser power can be reduced, a commercially available inexpensive and stable semiconductor laser can be used.

(3) Since the temperature of the laser irradiation part can be kept low, the characteristic deterioration due to thermal damage can be reduced.

(4) The erasing ratio during overwriting can be dramatically increased.

[Brief description of the drawings]

FIG. 1 is a schematic view of a multi-phase recording layer of an information recording medium of the present invention.

[Explanation of symbols]

 1: Phase transition phase 2: Non-phase transition phase

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-64-72341 (JP, A) JP-A Sho 64-72340 (JP, A) JP-A-3-104019 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24

Claims (2)

(57) [Claims] In a recording method for recording information by causing a phase change in a recording layer material by irradiating a light beam, a main component of the recording layer is a crystal-to-amorphous or crystal-to-crystal during recording. (M phase) that causes phase transition of
And a phase (L phase) in which no phase transition occurs during recording , and an M phase and an L phase satisfy the following conditions by irradiating a laser beam having a recording power to the information recording medium, and thereby forming an L phase. Is a method for recording information by causing a phase transition from a crystalline state or an amorphous state to an M phase without causing a phase transition. However, the relationship between the M phase and the L phase is L _1−a + M _a (0.30 ≦ a ≦ 0.92). 2. An erasing method for erasing information by irradiating a light beam to cause a phase change in a material of a recording layer and erasing information. (M phase) that causes phase transition of
A laser beam having an erasing power is applied to an information recording medium that exists in a mixed phase state of a phase that does not cause a phase transition at the time of erasing (L phase) and the M phase and the L phase satisfy the following conditions. Is a method of erasing information by causing a phase transition from a crystalline state or an amorphous state to an M phase without causing a phase transition. However, the relationship between the M phase and the L phase is L _1−a + M _a (0.30 ≦ a ≦ 0.92).